Apparatus for transporting moldings from an injection molding machine
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an apparatus for transporting from an injection molding machine the moldings which have been produced by injection molding and are received by molding receptacles, which are filled in a filling station disposed adjacent to the injection molding machine and are transferred to transporting means by transfer means. 
     2. Description of the Prior Art 
     A known apparatus of that kind is disclosed in U.S. Pat. No. 4,737,095. In that known apparatus the moldings falling out of the injection mold are placed by means of conveyor belts into a molding receptacle, which is disposed in a filling station. When the molding receptacle has been filled, it is transferred to a truck, which is movable on a linear path, which is parallel to the vertical longitudinal plane of symmetry of the injection molding machine. That truck is also designed for a transportation of injection molds which have been or are to be used in the injection molding machine and the truck can transport a molding receptacle and an injection mold at the same time. Although the transport from the machine can thus be rationalized, there may be bottlenecks of time if numerous transport movements are to be performed, particularly because only a single truck can travel, as a rule, on the associated track. 
     It is also known (NL 83 02 899) to provide an apparatus for stacking stackable injection moldings, which in dependence on their periodic discharge from the injection mold are supplied via a chute individually or in groups. By means of two decks, the arriving moldings are moved in alternation to positions over a stacking apparatus and are then consectively released from suction cups in registry with a columnar stack. The columnar stack composed of the superimposed moldings is then moved on a horizontal path into a magazine which is associated with the apparatus. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an apparatus which is of the kind described first hereinbefore and which is so improved that the required operating time of the means for transporting the molding containers can greatly be reduced and the transfer means of the apparatus are designed for a transport of full pallets from the filling station and for a supply of empty pallets to the filling station. 
     That object is accomplished in accordance with the invention in that the molding receptacles consist of stackable pallets, a pallet tower is included in the apparatus and comprises an elevator, which is movable along vertical skeleton elements of the pallet tower, the stackable pallets are movable from pallet tracks of the filling station into the pallet tower and in the pallet tower are adapted to be coupled to a handling pallet, which is supported on the elevator, to form a load unit, and the elevator is adapted to contain at least one load unit comprising full stackable pallets and at least one additional load unit comprising empty stackable pallets. 
     In such an apparatus, load units can be formed by periodic vertical movements of the elevator loaded with full stackable pallets 55 and said load units can be pulled out of the pallet tower on the rear. On the other hand, empty stackable pallets will always be available in the pallet tower and can periodically be moved into the filling station. Such empty stackable pallets have been supplied in the form of load units to the pallet tower from the rear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view showing the apparatus in association with an injection molding machine with the filling station for the molding receptacle disposed within the vertical projection of the injection molding machine. 
     FIGS. 2 and 3 are, respectively, a top plan view and an end elevation showing the apparatus which has been integrated in the injection molding machine. 
     FIGS. 4 and 5 illustrate a variant of the apparatus with the filling station disposed outside the vertical projection of the injection molding machine. 
     FIGS. 6 to 8 are enlarged views taken in different directions and showing a stackable pallet which constitutes a molding receptacle of the apparatus. 
     FIGS. 9 to 11 show a handling pallet and respective stacks consisting eahc of a plurality of stackable pallets carried by said handling pallet. 
     FIGS. 12a to 12f and 12a&#39; to 12f&#39; are diagrammatic representations illustrating the automatically performed stacking operation for forming load units consisting each of a stack and a handling pallet. 
     FIGS. 13 and 14 are, respectively, a vertical sectional view and a fragmentary horizontal sectional view showing a modified stackable pallet for use in the apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Illustrative embodiments of the invention will now be explained more in detail with reference to the drawing. 
     The apparatus in accordance with the invention is associated with an injection molding machine, which comprises a horizontal injecting unit S and a horizontal clamping unit W. Said two units are supported by a machine pedestal 10. The moldings 63 which have been formed by injection molding are removed from the injection molding machine by means of stackable pallets 55, which are filled in a filling station, which is disposed adjacent to the injection molding machine. In the illustrative embodiments of the invention the filling station is selectively disposed either within the injection molding machine, as is shown in FIGS. 1 to 3, or outside the machine adjacent to that end thereof which defines the clamping unit, as is shown in FIGS. 4 and 5. In the former case the stackable pallet 55 is filled by means of a demolding device H, which removes the moldings 63 from the injection mold when it is open and the moldings are placed in rows into and retained by recesses 55g (FIG. 7) by an intermittent movement of a gripper in a direction which is transverse to the longitudinal vertical plane of symmetry s--s of the machine. In the second case the stackable pallet 55 is filled by means of a belt conveyor 18, which transports the moldings along a path which is parallel to the plane of symmetry s--s. The moldings are placed on the belt conveyor 18 by the gripper of the demolding device. The stackable pallet 55 may alternatively be filled by a conveyor belt, which receives the moldings as they fall out of the injection mold when it is open, as is shown in FIG. 5. 
     The stackable pallets 55 are so designed that they can be stacked to form stacks in which the pallets center each other. The stackable pallets 55 are stacked to form stacks in a pallet tower 54, which is disposed between the filling station and another transport means, such as a truck or a roller conveyor. In the embodiment which is shown by way of example the pallet tower 54 is disposed on the rear of the injection molding machine outside the vertical projection of the machine. The pallet tower is placed on the floor and protrudes above the injection molding machine. The pallet tower 54 comprises a skeleton structure 54a, which consists of section members, inclusive of vertical skeleton members 54a&#39;, along which an elevator 54b is movable on rollers 54c. The skeleton structure 54a is provided with two pallet tracks, which will be described hereinafter as adjustable pallet tracks 59 because their spacing is adjustable. The stackable pallets 56 are movable from the filling station into the pallet tower 54 on stationary pallet tracks 58 and on the adjustable pallet tracks 59. By a vertical movement of the elevator 54b, which carries a handling pallet 56, the stackable pallets 55 can be coupled to said handling pallet 56 to form a load unit T; T&#39;; T&#34; as is shown in FIGS. 9 to 11. Each of the adjustable pallet tracks 59 is secured to the piston rod of a hydraulic cylinder 59a, which is supported on the skeleton structure 54a of the pallet tower 54. The drive means for displacing the stackable pallet 55 from the filling station into the pallet tower 54 and vice versa comprises an endless chain 57b, which is disposed below the stackable pallet 55 when it is in the filling station. As is apparent from FIG. 2 the pivot pins of the chain 57b, which constitutes a link chain, are vertical and at least one coupling pin 57a of the chain protrudes upwardly from the chain. By a semicircular movement of the chain 57b around the chain sprocket 57c that coupling pin 57a can be coupled to a stackable pallet 55 which is disposed in the filling station or in the pallet tower 54. The coupling is effected in that the coupling pin 57a is constrained to perform a lateral movement into a coupling element 55c, which is secured to the stackable pallet 55. The elevator 54b is rectangular in a top plan view and comprises four vertical tubular posts, which are interconnected by crosspieces. The elevator is vertically movable by a lifting screw 62a, which is supported by the skeleton structure 54a and can be rotated by a lifting motor 62. The screw 62a is screwed into a nut 62b, which is secured to the elevator. The stackable pallet 55 comprises a pallet bottom 55a, which is designed to retain the moldings 63 at fixed locations, which are arranged in rows. The moldings are retained in recessed 55g, which conform to respective moldings and are shown in FIG. 7. The bottom 55a is surrounded by a vertical guard wall 55f. As is particularly apparent from FIGS. 6 and 8 the vertical projection of the bottom 55a is smaller than the vertical protection of the guard wall. Besides, the bottom is connected to the vertical guard wall by a centering portion 55d, which is slightly inclined from the vertical (FIG. 6a). Each stackable pallet 55 comprises horizontal supporting surfaces 55h. The supporting surfaces 55h of the uppermost stackable pallet 55 of each stack rest on the guard wall 55f of the next lower stackable pallet. The uppermost stackable pallet extends into said next lower stackable pallet. Stackable pallets having guard walls equal in height can be stacked to form stacks which have the same overall dimensions. Each stack may comprise stackable pallets 55 having higher or lower guard walls and the number of stackable pallets in each stack will depend on the height of said guard walls. For instance, FIGS. 9 to 11 illustrate stacks which consist of two, three and six stackable pallets, respectively. Each stack is supported on and centered by a handling pallet 56 to form a load unit therewith. The handling pallet 56 comprises a profiled supporting surface, which is complementary to the profiled supporting surface of an injection mold 14a, 14b. That profiled supporting surface of the handling pallet 56 is constituted by two parallel track rails 56b, which are interconnected by at least one crosspiece. The track rails 56b have the same shape in cross-section as the engaging plates 14a&#39;, 14b&#39; of the injection mold 14a, 14b shown in FIGS. 9 and 10. The purpose of said equality of shape will be set forth hereinafter. 
     The height of the pallet tower 54 is more than twice the height of the elevator 54b, which in the embodiment shown by way of example can carry three superimposed load units T; T&#39;; T&#34;. In addition, the elevator 54b is adapted to support a plurality of handling pallets 56, which are spaced apart a distance which is at least as large as the height of a load unit. One of the three handling pallets 56 of the elevator 54b is designed to constitute a load unit T; T&#39; or T&#34; with full stackable pallets 55, which are filled with moldings 63. The two other handling pallets 56 are designed to constitute load units with empty stackable pallets 55. On a predetermined transfer level, which equals the level of the filling station, the load units can be moved out of and into the pallet tower 54 on the rear. The elevator 54b of the pallet tower also comprises over each handling pallet 56 a plurality of non-contacting signal generators 60 for a detection of pallets. The number of signal generators 60 provided over each handling pallet corresponds to the largest number of pallets which can be included in a stack. The spacing of the signal generators over each handling pallet equals the height of a stackable pallet having the lowest guard wall. A non-contacting signal generator 61 for detecting stackable pallets is also provided at the end of the filling station. The filling station shown in FIGS. 1 to 3 is disposed within the vertical projection of the injection molding machine. That embodiment can be converted with a relatively small amount of work to the embodiment which is shown in FIGS. 4 and 5 and in which the filling station is disposed outside the vertical projection of the injection molding machine in front of that end face of the injection molding machine at which the clamping unit W is disposed. For a conversion from the embodiment shown in FIGS. 1 to 3 to the embodiment shown in FIGS. 4 and 5 and vice versa it is substantially sufficient to replace the stationary pallet tracks 58 of the filling station by an endless belt conveyor 18, which is disposed on the same level as the stationary pallet tracks 58, and vice versa. The demolding device places the moldings 63 on the conveying surface of the conveyor belt 18 at locations which correspond to the locations at which the moldings are placed on stackable pallets in the embodiment shown in FIGS. 1 to 3. For this reason the stationary pallet tracks 58 of the filling station of the embodiment shown in FIGS. 1 to 3 and the conveying surface of the belt conveyor of the embodiment shown in FIGS. 4 and 5 extend approximately in the same horizontal plane, which is designated e-e in FIG. 3 and is approximately level with the top edge of the injection mold 14a, 14b. 
     The load units T; T&#39;, T&#34; which have been formed in the pallet tower 54 are transferred to the further transporting means, which preferably consist of a truck F, which is movable on a path that is parallel to the plane of symmetry s-s. The truck F which is shown in a schematic and fragmentary manner in FIGS. 12 and 12a and which has a transport chain F&#39; need not be described in detail here because a suitable truck is disclosed in U.S. Pat. No. 4,737,095. The known truck comprises guiding and retaining means for a selective handling of injection molds or load units simultaneously or in alternation. Each of said load units comprises a handling pallet, which has a profiled supporting surface which has the same shape as the profiled supporting surface of the injection mold. 
     The profiled shape of the engaging plates 14a&#39;, 14b&#39; of the injection mold is simulated by the track rails 56b of the handling pallet 56. The fact that the truck F can be used to carry load units and injection molds on the same supporting surfaces results in an important rationalization of the handling system associated with the injection molding machine. For that purpose the truck is provided with receiving and delivering means, which are intended to move the injection mold 14a, 14b or a load unit (which according to the prior art consists of a handling pallet and a plasticizing cylinder) in a direction which is transverse to the direction of travel of the truck. The receiving and delivering means comprise driving and displacing means, which preferably consist of an endless conveyor chain. With that design, load units comprising full stackable pallets can be pulled out of the pallet tower 54 onto the truck and load units comprising empty stackable pallets can be pushed from the truck into the pallet tower 54. For said delivering and receiving operations the receiving and delivering means of the truck comprise an endless chain, which is provided with at least one coupling pin. The handling pallet 56 has at least one track rail 56b, which is provided with a transverse groove 56a and the coupling pin of the chain can be moved into the transverse groove 56c for a coupling operation and can be moved out of said groove for an uncoupling operation. 
     Concrete operations by which the load units T; T&#39;; T&#34; comprising the handling pallets 55 are assembled are apparent from FIGS. 12a to 12f. FIG. 12a shows the full stackable pallet 55&#39;, which is still disposed adjacent to the injection molding machine. Two load units which comprise an empty handling pallet 56 and stackable pallets 55 are arranged in the top portion of the elevator in the pallet tower 54. 
     It is apparent from FIG. 12b that the full stackable pallet 55&#39; has been pushed from the filling station onto the adjustable tracks 59 of the pallet tower and the elevator 54b has subsequently been raised a small distance so that the empty handling pallet 56 has engaged the underside of the stackable pallet 55&#39; which has been inserted and the handling pallet 56 has thus been centered. By means of the hydraulic cylinders 59a the pallet tracks 59 are then moved further apart so that the elevator is free for a vertical movement. The lifting screw drive 62a, 62b is then operated to raise the elevator 54b to the position which is shown in FIG. 12c and in which the empty uppermost stackable pallet 55 of the next upper load unit is on the same level as the pallet tracks 59, which have been moved to have a large spacing. Thereafter the pallet tracks 59 are moved to have a small spacing so that they support the uppermost stackable pallet 55. Before that empty stackable pallet 55 can be moved into the filling station, the empty stackable pallet 55 must be separated from the associated pallet stack. For that purpose the elevator is lowered until the stackable pallet is free to perform a horizontal movement. The drive means 57 are then operated to move the empty stackable pallet 55 on the pallet tracks 58, 59 into the filling station, in which the pallet 55 rests on the stationary pallet tracks 58 in the position which is shown in FIG. 12c and in which the stackable pallet is filled in the filling station. When the adjustable pallet tracks 59 have then been adjusted to have a large spacing, the elevator 54b is raised to the position which is shown in FIG. 12d and in which another full stackable pallet 55&#39; can be moved into the elevator so that the position shown in FIG. 12e is assumed. By a slight vertical movement of the elevator the handling pallet 56 on which a stackable pallet 55 has been placed is moved to such a position that both full stackable pallets 55&#39; are in a stacked position, in which the guard wall of the lower full stackable pallet 55&#39; surrounds the bottom of the upper full stackable pallet 55&#39; so as to center the latter. The adjustable pallet tracks 59 are then moved to have a large spacing so that the elevator is again free to perform a vertical movement. The elevator is then lowered to the position shown in FIG. 12f, etc. Consecutive load units T; T&#39;; T&#34; are assembled by the process steps described. When a load unit has been assembled, that load unit is pulled out from the pallet tower 54 at the rear and is transferred onto the truck. When all empty stackable pallets have been used to form load units, the truck is operated to supply load units comprising empty stackable pallets to the pallet tower so that the position shown in FIG. 12a will be achieved. The non-productive times can be reduced because two load units comprising empty stackable pallets are available in the pallet tower. Such non-productive times would otherwise occur whenever all empty stackable pallets of the pallet tower have been consumed and a load unit comprising full stackable pallets must be removed from the tower before a load unit comprising empty stackable pallets can be moved into the pallet tower. For the procedure which has been described it makes no difference whether the two load units comprising empty stackable pallets are disposed over or under the load unit which includes full stackable pallets and is just being assembled. The stacks comprising empty stackable pallets will usually be disposed in alternation over and under the stack which is to be assembled from full stackable pallets. 
     As is apparent from FIG. 2 the track rails 56b of the handling pallets 56 are supported on horizontal skeleton members 54a&#34; of the skeleton structure 54a as the load units T; T&#39;; T&#34; are moved out of and into the pallet tower 54. 
     For a detection of pallets in the pallet tower, the signal generators 60 inductively cooperate with code noses 55e of the stackable pallets 55. In each stack, the uppermost stackable pallet 55 is supported at its supporting surfaces 55h (FIG. 6a) on the top edge of the guard wall of the next lower stackable pallet. The endless chain 57b of the drive means 57 in the filling station is driven by the drive motor 57d, as is shown in FIG. 3. During their displacement into and out of the pallet tower 54 the stackable pallets 55 are supported at their guide bars 55b on the pallet tracks 58, 59. 
     FIGS. 13 and 14 show a different stackable pallet 155, which can more easily be stacked in the pallet tower 54. In that embodiment the two walls 155a which are parallel to the direction in which the pallet is displaced have outwardly offset end portions 155a&#39;. Horizontal supporting surfaces are provided at the base of the end portion and constitute pallet tracks 159 for guiding a full stackable pallet 155&#39; coming from the stationary pallet tracks 58 of the filling station or for guiding an empty stackable pallet 155 which is to be transferred from the pallet tower 54 into the filling station. 
     The crosspiece 56c of the handling pallet 56 is provided with longitudinal tracks, which are arranged and designed to conform to the track-forming end portions 155a&#39; of the walls 155a of the stackable pallets 155. In each load unit, the lowermost stackable pallet 155 of the stack to be formed is supported and guided on and centered by the handling pallet 56, which is supported on the elevator 54b. Each upper stackable pallet 155 is supported on and guided on and centered by the next lower stackable pallet 155. For this reason the adjustable pallet tracks 59, which in the embodiment shown in FIGS. 1 and 12 are supported on the skeleton structure 54a, and the means for actuating said adjustable tracks 59, are eliminated. The load unit in which each stackable pallet 155 is guided by the pallet tracks 159 of the next lower stackable pallet 155 or of the longitudinal tracks of the handling pallet can be assembled substantially like the load unit comprising the stackable pallets 55 as shown in FIG. 6 to 11. This may be explained with reference to FIGS. 12a&#39; to 12f&#39;: In the position shown in FIG. 12a&#39; a full stackable pallet 155&#39; is still in the filling station and two load units which contain empty stackable pallets 155 are provided over an empty handling pallet 56 in the pallet tower 54 in the elevator. 
     In the position shown in FIG. 12b&#39; the full stackable pallet 155&#39; has been pushed from the filling station into the pallet tower 54 on pallet tracks of the handling pallet 56. Said pallet tracks are shaped and arranged to correspond to the pallet tracks 159 of the stackable pallets 155 (FIGS. 13 and 14). 
     In the position shown in FIG. 12c&#39; the elevator has been lowered to such a position that the uppermost empty stackable pallet 155 of the next upper load unit is on the level of the stationary pallet tracks 58 of the filling station and the uppermost empty stackable pallet 155 has already been moved from the pallet tower to the filling station and rests therein on the pallet tracks 58. As said empty stackable pallet is filled, the elevator is raised to the position which is shown in FIG. 12d&#39; and in which the stackable pallet in the filling station has already been filled. 
     In the position shown in FIG. 12e&#39; the full stackable pallet 155&#39; has been pushed out of the filling station to the stackable pallet which rests on the handling pallet 56. During that pushing into the pallet tower, the full stackable pallet is guided in part on the pallet tracks 58 of the filling station and in part on the tracks 159 of that full stackable pallet which rests on the handling pallet 56. 
     FIG. 12f&#39; shows the position which has been reached after a further process step, in which the elevator is lowered until the uppermost empty stackable pallet 155 of the next upper load unit containing empty stackable pallets is on the level of the pallet tracks 58 of the filling station and can be pushed out of the pallet tower 54 into the filling station to assume the position shown in FIG. 12f&#39;. In the sequence of operations which have been described the load units T; T&#39;; T&#34; are consecutively assembled. When a load unit comprising full stackable pallets 155&#39; has been assembled, that load unit is pulled out of the pallet tower 54 at the rear and is transferred to a truck, which is movable on a path which is parallel to the longitudinal vertical plane of symmetry s--s of the injection molding machine. 
     When the empty stackable pallets 155 of the respective load units in the pallet tower 154 have been consumed, additional load units comprising empty stackable pallets are supplied to the pallet tower by means of the truck so that the position shown in FIG. 12a&#39; has been obtained. 
     In the load units which comprise stackable pallets 155 as shown in FIGS. 13 and 14 said stackable pallets 155 will be held by frictional forces against a displacement along the tracks when an upper stackable pallet 155 is displaced on the slide tracks 159 of the next lower stackable pallet 155 or from the corresponding pallet tracks of the handling pallet 56. The magnitude of said frictional forces will be determined by the initial stress under which the end portions 155a&#39; of those walls 155a of the next lower stackable pallet 155 which extend along the pallet tracks bear on the corresponding walls 155a of the next upper stackable pallet 155. Said frictional forces are so determined that they can readily be overcome as that stackable pallet 155 which is disposed on the transfer level, i.e. on the level of the stationary pallet tracks 58 of the filling station, is to be pulled out of the pallet tower 54. In order to ensure that stackable pallets 155 disposed below that transfer level will not be pulled out of the stack together with the stackable pallet 155 which is on said transfer level, stationary vertical stop rods 65 shown in FIG. 2 are provided on the front and rear sides of the pallet tower in such positions that they prevent a horizontal displacement of all stackable pallets in the pallet tower, other than the stackable pallet 155 which is on the transfer level, along the pallet tracks.